"In some cases, the most intimate questions a person is asking—about health worries, relationship woes, financial hardship—are the ones that set off a chain reaction that can have troubling consequences both online and offline.

All this is because being online increasingly means being put into categories based on a socioeconomic portrait of you that’s built over time by advertisers and search engines collecting your data—a portrait that data brokers buy and sell, but that you cannot control or even see."